C3- the periodic table Flashcards
What was the law of octaves and who put it forward?
An English scientist called John Newlands put forward his Law of Octaves in 1864. He arranged all the elements known at the time into a table in order of relative atomic mass.
When he did this, he found a pattern among the early elements. The pattern showed that each element was similar to the element eight places ahead of it. He then put the similar elements into vertical columns, known as groups.
Why was John Newlands’ table not accepted by other scientists?
Newlands’ table showed a repeating or periodic pattern of properties, but this pattern eventually broke down. By ordering strictly according to atomic mass, Newlands was forced to put some elements into groups which did not match their chemical properties
Who else created a periodic table based on ordering the elements by relative atomic mass?
In 1869, just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table. Mendeleev also arranged the elements known at the time in order of relative atomic mass. But he also realised that the physical and chemical properties of elements were related to their atomic mass in a ‘periodic’ way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
Why did Dmitri Mendeleev leave gaps in his table?
Sometimes this method of arranging elements meant there were gaps in his horizontal rows or ‘periods’. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered.
What factors gave more success to Mendeleev’s table?
Despite leaving gaps, he was able to work out the atomic mass of the missing elements, and so predict their properties. And when they were discovered, Mendeleev turned out to be right.
What were the similarities of Newlands and Mendeleev’s tables?
Both Ordered elements by atomic weight.
What were the differences of Newlands’ and Mendeleev’s tables?
Newlands table only included the elements known at the time, whilst Mendeleev left gaps for elements he predicted would be discovered later. Newland maintained a strict order of atomic weights whilst Mendeleev Swapped the order of some elements if that fitted their properties better.In Newlands’ table every eighth element had similar properties, but in Mendeleev’s table elements in groups had similar properties.
How did people react to Newlands’ table?
Was criticised by other scientists for grouping some elements with others when they were obviously very different to each other
How did people react to Mendeleev’s table?
Was seen as a curiosity to begin with, but then as a useful tool when the predicted elements were discovered later
What was the problem about ordering the elements with atomic mass?
It could be difficult for Mendeleev to group elements in similar properties, for example: iodine has a lower relative atomic mass than tellurium, so it should come before tellurium in Mendeleev’s table.In order to get iodine in the same group as other elements with similar properties - such as fluorine, chlorine and bromine - he had to put it after tellurium, which broke his own rules
What was discovered that allowed Mendeleev’s table to be refined?
the discovery of protons, neutrons and electrons in the early 20th century allowed Mendeleev’s table to be refined into the modern periodic table.It involved an important modification – the use of atomic number to order the elements.
Who proposed the idea of using atomic number to order the elements and why?
Using atomic number instead of atomic mass as the organising principle was first proposed by the British chemist Henry Moseley in 1913. It explained why Mendeleev needed to change the order of some of the elements in his table.
Why do elements in the same group have similar properties?
The elements in a group all have the same number of electrons in their highest occupied energy level (also referred to as the outer shell). This is why they have similar chemical properties.
What are the group 1 elements called?
The alkali metals.
What are the properties of alkali metals?
they are very soft and can be cut easily with a knife
they have low densities (lithium, sodium and potassium will float on water)
they react quickly with water - producing hydroxides and hydrogen gas
their hydroxides dissolve in water to form alkaline solutions
low melting points and boiling points compared to other metals.
What is the equation for the reaction between an alkali metal and water?
group 1 metal + water → group 1 metal hydroxide + hydrogen
2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)
(M stands for the symbol of a Group 1 metal)
What happens as you go down the group 1 metals?
They get more reactive.
What are the ionic compounds that group 1 metals produce?
The ionic compounds produced are white solids which form colourless solutions when they dissolve.
What are the elements between groups 2 and 3 called?
The transition metals.
What are the properties of transition metals?
They are high density they have a high melting point they have low reactivity (not very reactive with water, air or acid) They are strong and hard They make coloured compounds
What do many transition metals act as?
A catalyst.
How do you make ammonia?
You react hydrogen with nitrogen over an iron catalyst to form ammonia, in a reversible reaction.
What are the group 7 elements called?
halogens
What are the common properties of Halogens?
they are non-metals
they have low melting and low boiling points
they are brittle when solid
they are poor conductors of heat and electricity
they have coloured vapours
their molecules are diatomic (each contain two atoms)
they are toxic
What happens as you go down the elements in group 7?
The melting and boiling points increase, and the colours of the elements become darker and the halogens become less reactive.
What are the common colours of group 7 elements?
Fluorine is very pale yellow, chlorine is yellow-green and bromine is red-brown. Iodine crystals are shiny purple-black but easily turn into a dark purple vapour when they are warmed up.
What happens during displacement reactions in the halogens?
In these reactions, a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
What does the reactivity of an element depend on?
The reactivity of an element depends on how easily its atoms lose or gain electrons.
Why do elements in group 1 get more reactive as you go down the group?
elements in Group 1 lose the electron from their highest occupied energy level (outer shell) to form ions with a +1 charge.
As you go down the group, the number of occupied energy levels (filled shells) increases. The higher the energy level of the outer electrons, the greater the distance from the nucleus, and the more easily electrons are lost
Why do elements in group 7 get less reactive as you go down the group?
elements in Group 7 gain one electron into their highest occupied energy level (outer shell) to form ions with a –1 charge.
As you go down the group, the number of occupied energy levels (filled shells) increases. The higher the energy level of the outer electrons, the greater the distance from the nucleus, and the less easily electrons are gained.
